Secondary air supply device and method for internal combustion engine

ABSTRACT

A secondary air supply device for an internal combustion engine includes an air pump that can be actuated while the internal combustion engine is stopped. An air passage connects the air pump and an exhaust passage of the internal combustion engine and an air supply control section controls the air pump so as to switch the air pump from a stopped state to an actuation state a predetermined time after the internal combustion engine is stopped. The secondary air supply device utilizes an air supply system including the air pump and the air passage to supply air to the exhaust passage.

INCORPORATION BY REFERENCE

This document claims priority to Japanese Application No. 2007-206753, filed on Aug. 8, 2007, the entire content of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a secondary air supply device and method for an internal combustion engine that utilizes an air pump to supply air to an exhaust passage of the internal combustion engine.

2. Description of the Related Art

Japanese Patent Application Publication No. 6-117234 (JP-A-6-117234) discloses a secondary air supply device for an internal combustion engine. The secondary air supply device includes an air pump that supplies air to an exhaust passage of the internal combustion engine, and an air passage that connects the air pump and the exhaust passage. The air pump is actuated for a predetermined time after the internal combustion engine is sensed to be stationary. Another example is disclosed in Japanese Patent Application Publication No. 6-17645 (JP-A-6-17645).

With the device disclosed in JP-A-6-117234, the air pump is actuated, with the actuation continuing for a predetermined time after the internal combustion engine is stopped, so that condensed water produced in the air pump due to the condensation of water contained in exhaust gas reversed from the exhaust passage while the air pump is stationary can be drained. However, condensed water is occasionally produced in an air supply system, which includes the air pump and the air passage, as the air supply system is cooled after the condensed water in the air pump is drain. With the device disclosed in JP-A-6-117234, the air pump is merely actuated for a predetermined time after the internal combustion engine is stopped, and therefore it may not be possible to drain condensed water produced in the air supply system after the actuation of the air pump is finished.

SUMMARY OF THE INVENTION

According to one feature or advantage of the present invention, a secondary air supply device and method for an internal combustion engine is provided that can efficiently drain or remove condensed water produced in an air supply system after the internal combustion engine is stopped.

According to a first example of the present invention, a secondary air supply device for an internal combustion engine is provided which includes: an air pump that can be actuated while the internal combustion engine is stopped; an air passage that connects the air pump and an exhaust passage of the internal combustion engine; and an air supply control section that controls the air pump so as to switch the air pump from a stationary or stopped state to an actuation state a predetermined time after the internal combustion engine is stopped. The secondary air supply device utilizes an air supply system including the air pump and the air passage to supply air to the exhaust passage.

In the above first example, condensed water may be produced in the air supply system during at least a portion of the predetermined time.

According to the above example, it is possible to drain or remove from the air supply system not only condensed water existing in the air supply system when the internal combustion engine is stopped, but also condensed water produced in the air supply system after the internal combustion engine is stopped. Hence, it is possible to reliably prevent condensed water from collecting in the air supply system after the internal combustion engine is stopped. This can avoid malfunction of the air supply system due to freezing of condensed water even in environments with outside temperatures below freezing, for example, which improves the reliability of the device. It should be noted that the location to which the condensed water produced in the air supply system is removed or drain is not specifically limited, and the condensed water may be drain or removed into the exhaust passage or a passage separately provided for the drainage of the condensed water.

A second example of the present invention provides a secondary air supply device for an internal combustion engine including: an air pump that can be actuated while the internal combustion engine is stationary (in other words, stopped or off); an air passage that connects the air pump and an exhaust passage of the internal combustion engine; and an air supply control section that controls the air pump so as to switch the air pump from a stationary state to an actuation state after a condition relating to production of condensed water in the air supply system is satisfied after the internal combustion engine is stopped. The secondary air supply device utilizes an air supply system including the air pump and the air passage to supply air to the exhaust passage.

A third example of the present invention provides a control method for a secondary air supply device for an internal combustion engine that utilizes an air supply system to supply air to an exhaust passage of the internal combustion engine. The air supply system includes an air pump that can be actuated while the internal combustion engine is stopped, and an air passage that connects the air pump and the exhaust passage. The control method includes determining whether a predetermined time has elapsed after the internal combustion engine is stopped; and after the predetermined time, controlling the air pump to switch the air pump from a stopped state to an actuation state. The predetermined time is set as a time during which condensed water can be produced in the air supply system.

According to the above example, the air pump is switched from the stopped state to the actuation state, either a predetermined time (during which condensed water can be produced in the air supply system, for example) after the internal combustion engine is stopped, or after a condition relating to production of condensed water in the air supply system is satisfied after the internal combustion engine is stopped. Therefore, it is possible to drain or remove from the air supply system not only condensed water existing in the air supply system when the internal combustion engine is stopped, but also condensed water produced in the air supply system after the internal combustion engine is stopped. Hence, it is possible to reliably prevent condensed water from collecting and remaining in the air supply system after the internal combustion engine is stopped. This can avoid malfunction of the air supply system due to freezing of condensed water even in environments with outside temperatures below freezing, for example, which improves the reliability of the device.

As should be apparent, the invention can provide a number of advantageous features and benefits. It is to be understood that, in practicing the invention, an embodiment can be constructed to include one or more features or benefits of embodiments disclosed herein, but not others. Accordingly, it is to be understood that the preferred embodiments discussed herein are provided as examples and are not to be construed as limiting, particularly since embodiments can be formed to practice the invention that do not include each of the features of the disclosed examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a diagram schematically showing an internal combustion engine to which a secondary air supply device in accordance with a first embodiment of the present invention can be applied;

FIG. 2 is a timing chart illustrating the respective states of an ECU, an air pump, an ASV (air switching valve), and a drain valve after the internal combustion engine is stopped in accordance with the first embodiment of the present invention;

FIG. 3 is a flowchart showing an example of the control routine for secondary air supply control in accordance with the first embodiment of the present invention; and

FIG. 4 is a flowchart showing an example of the reactivation time setting routine in accordance with a second embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

A description will hereinafter be made of a first example of an embodiment of the present invention. FIG. 1 schematically shows an example of an internal combustion engine to which a secondary air supply device in accordance with a first embodiment of the present invention can be applied. An internal combustion engine 1 is an inline-4 cylinder gasoline engine mounted on a vehicle as a driving power source, for example. It should be noted that only a single cylinder 2 and its associated components are shown in FIG. 1. An intake passage 3 of the internal combustion engine 1 inducts air according to the opening degree of a throttle valve (not shown). The air is distributed to each cylinder 2 through an intake manifold 4 as a component of the intake passage 3, and then taken into each cylinder 2 via an intake port 5 as a component of the intake passage 3.

In the illustrated example, cylinder 2 is provided with an ignition plug (not shown) with its tip directed into the cylinder 2. Each cylinder 2 is also provided with a piston 6 that reciprocally moves in the cylinder 2. A combustion chamber 7 is formed in the space surrounded by the top surface of the piston 6 and the inner wall of the cylinder 2. A fuel injection valve 8 that injects fuel into the intake port 5 is provided for each cylinder 2 of the internal combustion engine 1. An air-fuel mixture is introduced into the combustion chamber 7 as the fuel injection valve 8 injects fuel, and the air-fuel mixture is ignited by a spark discharged by the ignition plug. The air-fuel mixture is combusted to move the piston 6, and the motion of the piston 6 is converted into the rotational motion of a crankshaft (not shown) to be output from the internal combustion engine 1.

Exhaust gas from each cylinder 2 is guided to an exhaust port 10 as a component of an exhaust passage 9, merged through an exhaust manifold 11 as a component of the exhaust passage 9, and then guided to an exhaust gas purification device 12. The exhaust gas purification device 12 is a known catalytic converter having a three-way catalyst that purifies exhaust gas by oxidizing hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust gas while reducing nitrogen oxides (NOx). The exhaust gas purified by the exhaust gas purification device 12 is released to the atmosphere through a silencer (not shown). The internal combustion engine 1 is provided with an intake valve 13 and an exhaust valve 14 that respectively open and close the intake port 5 and the exhaust port 10. These valves 13 and 14 are individually driven to open and close at predetermined timings by a known valve driving mechanism 15 driven by the rotation of the crankshaft.

The internal combustion engine 1 is provided with a secondary air supply device 20 that supplies air to the exhaust passage 9 to burn HC components contained in the exhaust gas. In the illustrated example, the secondary air supply device 20 includes an electric air pump 21 that runs on a battery (not shown) as a power source, an air passage 22 that connects the air pump 21 and the exhaust passage 9 to guide air discharged from the air pump 21 to the exhaust passage 9, an air switching valve (ASV) 23 that functions as a valve that opens and closes the air passage 22, a reed valve 24 that prevents the exhaust gas from flowing back from the exhaust passage 9 toward the air pump 21, and a control device 25 that controls the operation of the air pump 21, the ASV 23, and other components as desired.

To the air pump 21 are connected an induction passage 26 that guides air via a filter 27 for air filtration, and a drain passage 28 that drains out condensed water collected inside the air pump 21. The drain passage 28 is provided with a drain valve 29 that is driven electromagnetically, for example, to open and close the drain passage 28. The combination of the drain passage 28 and the drain valve 29 functions as the drain section in this example of the present invention. The operation of the drain valve 29 is controlled by the control device 25. The air passage 22 is branched at its end connected to the exhaust passage 9 such that each branch is connected to each exhaust port 10. In the air passage 22 between the air pump 21 and the ASV 23 are provided a pressure sensor 30 that outputs a signal in accordance with the pressure in the air passage 22, and a temperature sensor 31 that outputs a signal in accordance with the passage wall temperature. The secondary air supply device 20 utilizes an air supply system composed of the air pump 21, the air passage 22, and the ASV 23 described above to supply air to the exhaust passage 9. That is, the air pump 21 is actuated with the air passage 22 opened by the ASV 23 so that the air discharged from the air pump 21 is supplied through the air passage 22 into the exhaust passage 9 (exhaust port 11).

In the illustrated example, the control device 25 includes an engine control unit (ECU) 32 that can appropriately control the operating state of the internal combustion engine 1, and an activation timer 33 that can activate the ECU 32 if it has been suspended at a predetermined time. The ECU 32 is a computer including a microprocessor and peripheral devices such as a RAM and a ROM. The ECU 32 receives information on various operating parameters for the internal combustion engine 1 and executes various processes for the internal combustion engine 1. The ECU 32 receives a signal from an outside temperature sensor 34 that outputs a signal in accordance with the outside temperature, and also signals from the pressure sensor 30 and the temperature sensor 31 discussed above. Further, the ECU 32 receives a signal in accordance with the operating state of an ignition switch (IGSW) 35 which is operated to start and stop the internal combustion engine 1. Other sensors referenced by the ECU 32 include a coolant temperature sensor that outputs a signal in accordance with the temperature of the coolant of the internal combustion engine 1, and a crank angle sensor that outputs a signal in accordance with the engine speed, which are not shown in the drawing.

In this example, the secondary air supply device 20 is advantageously controlled by controlling the air pump 21 (and other components) after the internal combustion engine 1 is stopped. FIG. 2 is a timing chart illustrating the respective states of the ECU 32, the air pump 21, the ASV 23, and the drain valve 29 after the internal combustion engine 1 is stopped. As shown in FIG. 2, as the IGSW 35 is switched from ON to OFF to stop the internal combustion engine 1, the ECU 32 is accordingly stopped. When a reactivation time T1 has elapsed after that with the internal combustion engine has been stopped, the activation timer 33 automatically activates the ECU 32 at the time t1, and the drain valve 29 is accordingly opened. This allows the condensed water collected in the air pump 21 to be drain. The drain valve 29 is maintained open until a discharge time T2 (for example, 30 seconds) elapses after that. When the drain time T2 has elapsed, the drain valve 29 is switched to the closed state. When the drain valve 29 is switched to the closed state, the air pump 21 is switched from the stopped state to the actuation state and the ASV 23 is opened to open the air passage 22 at the time t2. This allows the air discharged from the air pump 21 to pass through the air passage 22, which allows the condensed water produced in the air supply system including the air pump 21 and the air passage 22 to be drain or removed to the exhaust passage 9. An actuation time T3 for the air pump 21 is preferably set to as short a time as possible during which the amount of remaining condensed water is reduced to a tolerable range (for example, 20 seconds), with the energy consumed by the air pump 21 taken into account. When the actuation time T3 has elapsed, the air pump 21 is switched to the stopped state, and the ASV 23 is switched to the closed state. Then, the ECU 32 is suspended. In a preferred example, it should be noted that the air pump 21 is feedback controlled, while it is being actuated, so as to decrease the deviation between the output value of the pressure sensor 30 and the target value for the pressure in the air passage 22.

The time since the internal combustion engine 1 is stopped until the air pump 21 is switched from the stopped state to the actuation state corresponds to the predetermined time in this example of the present invention. The amount of the condensed water in the air supply system is preferably at its maximum when the air pump 21 is switched from the stopped state to the actuation state. However, the condensed water produced in the air supply system may be in any amount, where such condensed water is produced at any degree. That is, the total of the reactivation time T1 and the drain time T2 may be set as the time during which condensed water can be produced in the air supply system.

In order to perform the above operation, the control device 25 executes the following control routine. FIG. 3 is a flowchart showing an example of the control routine for secondary air supply control. The program for this routine is stored in the ROM of the ECU 32, and read as the ECU 32 is activated to be executed repeatedly. First, in step S1, the control device 25 determines whether or not the ECU 32 has been activated by the activation timer 33. The process proceeds to step S2 if the ECU 32 has been activated by the activation timer 33, and to step S11 otherwise. In step S11, normal control is performed. That is, the control device 25 determines whether or not air can be supplied to the exhaust passable 9, and the air supply amount, according to the operating state of the internal combustion engine 1, and individually controls the operation of the air pump 21 and the ASV 23 according to the determination results.

In step S2, it is determined whether or not the value of a counter (or timer, in other words) ecdrnvo, which manages the elapsed time from the activation of the ECU 32, is less than the drain time T2. If the value of the counter ecdrnvo is less than the drain time T2, the process proceeds to step S3, where the drain valve 29 is opened to open the drain passage 28. Then, the counter ecdrnvo is incremented in step S4, before terminating the routine. On the other hand, if the value of the counter ecdrnvo is not less than the drain time T2, the process proceeds to step S5, where the drain valve 29 is closed to close the drain passage 28.

In step S6, it is determined whether or not the value of a counter ecaistim, which manages the elapsed time from the closure of the drain valve 29, is less than the activation time T3. If the value of the counter ecaistim is less than the activation time T3, the process proceeds to step S7, where the air pump 21 is switched from the stopped state to the actuation state, and in subsequent step S8, the ASV 23 is opened to open the air passage 22. After that, the counter ecaistim is incremented in step S9, before terminating the routine. On the other hand, if the value of the counter ecaistim is not less than the activation time T3, the process proceeds to step S10 to perform a termination process. That is, the control device 25 switches the air pump 21 being actuated to the stopped state, closes the ASV 23, and stops the ECU 32, before terminating the routine.

In the illustrated example, the control device 25 functions as the air supply control section of the present invention by executing the routine of FIG. 3, and functions as the drain control section of the present invention by executing steps S3 and S4 of FIG. 3.

According to the above embodiment, it is possible to drain or remove not only condensed water existing in the air supply system when the internal combustion engine 1 is stopped, but also condensed water produced in the air supply system after the internal combustion engine 1 is stopped. In addition, since the condensed water in the air pump 21 is drain from the drain passage 29 before the air pump 21 is switched to the actuation state, it is possible to prevent the condensed water inside the air pump 21 from splashing into the air passage 22 and so forth along with the actuation of the air pump 21.

A description will next be made of a second example of an embodiment of the present invention. This embodiment includes an alternative as to how to set the activation time, and is the same as the first embodiment except therefor. Thus, the description of the first embodiment is referred to as appropriate for the configuration of the internal combustion engine 1 and the secondary air supply device 20 and the details of the secondary air supply control. FIG. 4 is a flowchart showing an example of the reactivation time setting routine that is used to set the reactivation time T1. The program for this routine is stored in the ROM of the ECU 32, and read at appropriate times to be executed repeatedly. First, in step S21, the control device 25 acquires a passage wall temperature etpipe of the air passage 22 based on the signal from the temperature sensor 31. It should be noted that the passage wall temperature etpipe may be acquired by estimation, for example, based on various parameters such as the load of the internal combustion engine 1, the rotational speed thereof, and the actuation history of the secondary air supply device 20. Next, in step S22, the outside temperature is acquired based on the signal from the outside temperature sensor 34. The passage wall temperature etpipe and the outside temperature are both associated with cooling of the air supply system after the internal combustion engine 1 is stopped. That is, as the passage wall temperature etpipe is higher, the time for the air supply system to be cooled to a temperature at which condensed water is produced is longer. In addition, as the outside temperature is lower, the time for the air supply system to be cooled to that temperature is shorter. In other words, the time for condensed water to be produced after the internal combustion engine 1 is stopped varies according to these temperatures at the time when the internal combustion engine 1 is stopped.

Thus, if it is determined in subsequent step S23 that the internal combustion engine 1 is stopped, that is, the IGSW 35 is OFF, the process proceeds to step S24, where the reactivation time T1 is calculated based on the passage wall temperature etpipe and the outside temperature. The reactivation time T1 can be calculated by experimentally preparing a map having as variables the passage wall temperature etpipe and the outside temperature to provide the reactivation time T1, preliminarily storing the map in the ROM of the ECU 32, and referencing the map in combination with the values acquired in steps S21 and S22. If it is determined in step S23 that the IGSW 35 is not OFF, the subsequent processes are skipped, before terminating the routine.

In step S25, the activation timer 33 is set to the reactivation time T1, before terminating the routine. This causes the activation timer 33 to activate (or wake up) the ECU 32 being suspended (or sleeping) as the reactivation time T1 elapses.

According to the routine of FIG. 4, the reactivation time T1 is set every time the internal combustion engine 1 is stopped according to the status before the internal combustion engine 1 is stopped. Thus, the reactivation time T1 can be set appropriately with the status before the internal combustion engine 1 is stopped, and therefore the condensed water in the air supply system can be efficiently drain or removed by executing the routine for secondary air supply control of FIG. 3. In this example of an embodiment, the total of the reactivation time T1 and the drain time T2 discussed above corresponds to the predetermined time of the present invention. It should be noted that since the passage wall temperature and the outside temperature are both associated with cooling of the air supply system, the predetermined time may be set based on at least one of the passage wall temperature or the outside temperature.

The control device 25 functions as the temperature acquisition section in this example of the present invention by executing steps S21 and S22 of FIG. 4, and functions as the time setting section in this example of the present invention by executing step S24 and the routine of FIG. 3.

The present invention is not limited to the embodiments described above, and may be modified in various ways. Although the drain valve 29 is operated to drain the condensed water in the air pump 21 before the air pump 21 is switched to the actuation state, such an operation is not essential. Thus, the air pump 21 may be switched from the stopped state to the actuation state a predetermined time after the internal combustion engine 1 is stopped without performing such an operation.

The drain time T2 and the reactivation time T1 discussed above may be constant, or may be varied according to the amount of condensed water generated after the internal combustion engine 1 is stopped.

To drain the condensed water in the air pump 21, the air pump 21 may be actuated after a predetermined time elapses with the drain valve 29 maintained open and with the ASV 23 closed. In this case, the condensed water in the air pump 21 can be compulsorily drain of the drain passage 28 by actuating the air pump 21, and therefore the condensed water can be more reliably drain.

A description will next be made of a third example of an embodiment of the present invention. In contrast to the first and second embodiments, in which the timings at which the ECU 32 is reactivated, the drain valve 29 is opened and closed, and the air pump 21 is switched from the stopped state to the actuation state are controlled based on the times T1, T2, and T3, the above-mentioned timings are determined based on temperatures such as the passage wall temperature etpipe of the air passage 22 and the outside temperature in this embodiment.

In this embodiment, the air pump is switched from the stopped state to the actuation state in the case where a condition relating to production of condensed water in the air supply system is satisfied after the internal combustion engine 1 is stopped. Here, the condition relating to production of condensed water may be considered to be satisfied in the case where a temperature associated with cooling of the air supply system after the internal combustion engine 1 is stopped, such as the passage wall temperature etpipe of the air passage 22, the outside temperature, and the temperature of the coolant of the internal combustion engine 1, has been lowered to a temperature at which condensed water is produced. The operating condition before the internal combustion engine is stopped may be used to determine whether or not the condition relating to production of condensed water is satisfied. The ECU 32 may be reactivated and the drain valve 29 may be opened when the temperature associated with cooling of the air supply system reaches a predetermined temperature.

By way of example, according to an advantageous feature of embodiments of the present invention, the secondary air supply device may include a temperature acquisition section that acquires a temperature associated with cooling of the air supply system after the internal combustion engine is stopped, and a time setting section that sets the predetermined time based on the temperature acquired by the temperature acquisition section. The state of the condensed water produced in the air supply system varies according to the cooling state of the air supply system. With this feature, the air pump is switched from the stopped state to the actuation state at a time commensurate with the cooling state of the air supply system. This makes it possible to avoid unnecessarily increasing the length of the predetermined time in order to ensure that condensed water is drain, which provides efficient removal of condensed water.

Further by way of example, according to one of the advantageous features of the present invention, the temperature associated with cooling of the air supply system may be any temperature of which changes vary the cooling state of the air supply system such as cooling rate. For example, the temperature acquisition section may acquire as the temperature associated with the cooling at least one of the passage wall temperature of the air passage and the outside temperature at the time when the internal combustion engine is stopped. When the passage wall temperature at the time when the internal combustion engine is stopped is higher, the time for the air supply system to be cooled to a temperature at which condensed water is produced is longer. When the outside temperature at the time when the internal combustion engine is stopped is lower, the time for the air supply system to be cooled to that temperature is shorter. In other words, variations in these temperatures vary the cooling state of the air supply system after the internal combustion engine is stopped. According to this feature, a predetermined time reflecting the status before the internal combustion engine is stopped can be set every time the internal combustion engine is stopped.

Also by way of example, according to another advantageous feature of the present invention, the secondary air supply device may further include a drain section that can drain condensed water collected in the air pump, and a drain control section that controls the drain section such that the condensed water collected in the air pump can be drain before the air supply control section switches the air pump from the stopped state to the actuation state. With this feature, the condensed water in the air pump can be drain before the air pump is switched to the actuation state. Therefore, it is possible to prevent the condensed water in the air pump from splashing into the air passage after the air pump is switched to the actuation state.

According to another advantageous feature of the present invention, by way of example, the secondary air supply device may further include a valve that opens and closes the air passage, and the drain control section may individually control the valve and the air pump so as to actuate the air pump with the air passage closed by the valve. With this feature, condensed water can be compulsorily drain or forced out of the air pump by the actuation of the air pump. Hence, the condensed water in the air pump can be more reliably drain or removed.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

1. A secondary air supply device for an internal combustion engine, comprising: an air pump that can be actuated while the internal combustion engine is stopped; an air passage that connects the air pump and an exhaust passage of the internal combustion engine, wherein the secondary air supply device utilizes an air supply system including the air pump and the air passage to supply air to the exhaust passage; and an air supply control section that controls the air pump so as to switch the air pump from a stopped state to an actuation state a predetermined time after the internal combustion engine is stopped.
 2. The secondary air supply device according to claim 1, wherein condensed water is produced in the air supply system during at least a portion of the predetermined time.
 3. The secondary air supply device according to claim 1, further comprising: a temperature acquisition section that acquires at least one temperature associated with cooling of the air supply system; and a time setting section that sets the predetermined time based on the at least one temperature acquired by the temperature acquisition section.
 4. The secondary air supply device according to claim 3, wherein the temperature acquisition section acquires, as the temperature associated with the cooling, at least one of a passage wall temperature of the air passage or an ambient temperature.
 5. The secondary air supply device according to claim 4, wherein the temperature acquisition section acquires a passage wall temperature, and wherein the passage wall temperature is estimated based on at least one of a load of the internal combustion engine or a rotational speed of the internal combustion engine.
 6. The secondary air supply device according to claim 4, wherein the at least one temperature is estimated based on stored data relating to the secondary air supply device.
 7. The secondary air supply device according to claim 2, further comprising: a drain section that can drain condensed water collected in the air pump; and a drain control section that controls the drain section such that the condensed water collected in the air pump can be drained before the air supply control section switches the air pump from the stopped state to the actuation state.
 8. The secondary air supply device according to claim 7, further comprising: a valve that opens and closes the air passage, wherein the drain control section individually controls the valve and the air pump so as to actuate the air pump with the air passage closed by the valve.
 9. A secondary air supply device according to claim 1, wherein the predetermined time is variable, and wherein the air supply control section determines the predetermined time based upon at least one condition relating to an operating condition of the internal combustion engine or the air supply system.
 10. A secondary air supply device according to claim 1, wherein the predetermined time is variable, and wherein the air supply control section determines the predetermined time based upon at least one of a temperature of the air passage or an ambient temperature.
 11. A secondary air supply device according to claim 1, further comprising a valve that opens and closes the air passage, and wherein the air supply control section opens the valve at the same time as or after the air pump is switched to the activation state.
 12. A control method for a secondary air supply device for an internal combustion engine that utilizes an air supply system to supply air to an exhaust passage of the internal combustion engine, the air supply system including an air pump that can be actuated while the internal combustion engine is stopped, and an air passage that connects the air pump and the exhaust passage, the control method comprising: determining whether a predetermined time has elapsed after the internal combustion engine is stopped; and after the predetermined time, controlling the air pump to switch the air pump from a stopped state to an actuation state.
 13. The control method according to claim 12, wherein the air pump is switched to the actuation state after opening a drain valve to drain condensed water collected in the air pump and closing the drain valve.
 14. A secondary air supply device for an internal combustion engine, comprising: an air pump that can be actuated while the internal combustion engine is stopped; an air passage that connects the air pump and an exhaust passage of the internal combustion engine, the secondary air supply device utilizing an air supply system including the air pump and the air passage to supply air to the exhaust passage; and an air supply control means for controlling the air pump so as to switch the air pump from a stopped state to an actuation state a predetermined time after the internal combustion engine is stopped.
 15. A secondary air supply device for an internal combustion engine, comprising: an air pump that can be actuated while the internal combustion engine is stopped; an air passage that connects the air pump and an exhaust passage of the internal combustion engine, the secondary air supply device utilizing an air supply system including the air pump and the air passage to supply air to the exhaust passage; and an air supply control section that controls the air pump so as to switch the air pump from a stopped state to an actuation state after a condition relating to production of condensed water in the air supply system is satisfied after the internal combustion engine is stopped.
 16. The secondary air supply device according to claim 15, further comprising: a temperature acquisition section that acquires at least one temperature associated with cooling of the air supply system, and wherein the condition relating to production of condensed water is based on the acquired at least one temperature.
 17. The secondary air supply device according to claim 16, wherein the temperature acquisition section acquires as the temperature associated with the cooling at least one of a passage wall temperature of the air passage or an ambient temperature.
 18. The secondary air supply device according to claim 16, wherein the condition relating to production of condensed water is satisfied when the at least one acquired temperature is lower than a predetermined temperature.
 19. The secondary air supply device according to claim 16, wherein the condition relating to production of condensed water is satisfied when a predetermined time has elapsed after the internal combustion engine is stopped, and wherein the predetermined time is variable and is determined by the air supply control section based on the acquired at least one temperature.
 20. The secondary air supply device according to claim 15, further comprising: a drain section that can drain condensed water collected in the air pump; and a drain control section that controls the drain section such that the condensed water collected in the air pump can be drained before the air supply control section switches the air pump from the stopped state to the actuation state.
 21. The secondary air supply device according to claim 20, further comprising: a valve that opens and closes the air passage, wherein the drain control section individually controls the valve and the air pump so as to actuate the air pump with the air passage closed by the valve.
 22. A secondary air supply device according to claim 15, further comprising a valve that opens and closes the air passage, and wherein the air supply control section opens the valve at the same time as or after the air pump is switched to the activation state.
 23. A secondary air supply device according to claim 15, wherein the condition relating to production of condensed water is based on at least one of a temperature of the air passage or an ambient temperature. 